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APNG Specification: Difference between revisions
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make explicit that the boundaries of the animation are fixed to IHDR
Herbyderby (talk | contribs) m (fix typos) |
Herbyderby (talk | contribs) m (make explicit that the boundaries of the animation are fixed to IHDR) |
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An APNG stream is a normal PNG stream as defined in the [PNG Specification][pngspec], with three additional chunk types describing the animation and providing additional frame data. | An APNG stream is a normal PNG stream as defined in the [PNG Specification][pngspec], with three additional chunk types describing the animation and providing additional frame data. | ||
To be recognized as an APNG, an `acTL` chunk must appear in the stream before any `IDAT` chunks. The `acTL` structure is described in the next section. | To be recognized as an APNG, an `acTL` chunk must appear in the stream before any `IDAT` chunks. The `acTL` structure is described in the next section. | ||
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Subsequent frames are encoded in `fdAT` chunks containing almost the same structure of content as `IDAT` chunks. Information for each frame about placement and rendering is stored in `fcTL` chunks. The full layout of `fdAT` and `fcTL` chunks is described below. | Subsequent frames are encoded in `fdAT` chunks containing almost the same structure of content as `IDAT` chunks. Information for each frame about placement and rendering is stored in `fcTL` chunks. The full layout of `fdAT` and `fcTL` chunks is described below. | ||
The boundaries of the entire animation are specified by the width and height parameters of the PNG `IHDR` chunk, regardless of whether the default image is part of the animation. The default image should be appropriately padded with fully transparent pixels if extra space will be needed for later frames. | |||
== Chunk Sequence Numbers == | == Chunk Sequence Numbers == | ||